Kandler, in U.S. Pat. No. 3,214,355, teaches electrochemical impregnation of active battery material into electrode plaques. This process fills a rigid, sintered metallic powder plaque with active material by immersion in a 10% concentrated nickel nitrate solution, having a pH of 3, and electrolytic deposition of nickel hydroxide active material at a current density of about 1 milliampere (mA.)/sq.cm. After drying to reduce nickel hydroxide active material volume, cathodic polarization can be repeated. This process, however, is difficult to use with thick battery plaques. The electrodes produced by this process have an indicated capacity of 1 to 1.5 ampere-hours (Ah.)/sq. decimeter for plaque thicknesses of 0.65 mm.
Hardman, in U.S. Pat. No. 3,600,227, solved problems of thick plaque impregnation, and provided improved electrode capacity by using higher current densities during electrolytic deposition, preferably coupled with a current pulsing action, followed by an intermediate charging and discharging step. Hardman utilized expansible metal fiber plaques, and a saturated nickel-cobalt nitrate electrolyte solution having a pH of between 0.5 and 1.1. A series of current pulses was preferably used after the plaque was immersed in the nitrate electrolyte. Intermediate charging and discharging was used to form Ni(III) hydroxide, Ni(II) hydroxide, and finally Ni(III) hydroxide. This caused volume changes in the hydroxide active material, which opened up more pore volume in the expansible plaque. Further electrolytic deposition was then carried out at a current density of from about 20 to 100 mA./sq.cm. While this provided a capacity of about 5.7 to 7.1 ampere-hours/sq. decimeter or 0.37 to 0.46 ampere-hours/sq. inch of plaque area for a plaque thickness of 1.9 mm., some corrosion and metallic fiber dissolution problems were occassionally encountered. What is needed is a process to highly load thick battery plaques without corrosion and dissolution problems, in order to consistently yield high performance electrode plates.